1. Field of the Invention:
This invention relates to methods and apparatus for forming photographic images from digital data. Such systems are used, for example, to generate photographs from digital information collected by means of satellites, aircraft, or other sources. The digital information may be derived by scanning photographic prints or negatives. The digital information, after computer enhancement or other modification of the data, is reproduced in image form for use in such diverse applications as oil and mineral exploration, forestry and agricultural management, surveillance, map making, and scientific study of the environment, printing, art, and medical diagnosis.
2. Description of Related Art:
Digital imaging systems are in wide use for many applications Both black and white and full color systems have been developed. In both systems, it is common practice to use an uncollimated white light source. For color systems, the white light is separated into color components by filters. The separate beams are then intensity modulated in accordance with the digital information to be portrayed. A piece of photographic film is placed on a revolving drum where it is exposed to the modulated light beams. The photographic images are formed of small rectangular pixels that are individually exposed to the particular intensity and color called for by the digital data. In the typical color system, three separate beams of light are directed toward the film at different locations. The composite exposure of the three beams produces the appropriate color and intensity at each pixel location The quality of the prints made in this manner leaves something to be desired.
It is difficult to maintain the positioning of the three separate beams with such precision that each pixel, which must be subjected to three successive exposures, is clearly defined and abuts the adjacent pixels without overlapping. In addition to the difficulty of separately controlling the three separate light beams, the rotation of the drum must be maintained with great precision at a constant speed to prevent the pixels from either being spaced apart or overlapping.
The paths of the light beams, between the source and the film surface, must be controlled with high precision. The adjustment of these beam paths is a meticulous task usually requiring several hours of painstaking work.
The intensities of the colored light beams, after separation from the white source beam, are low and require the use of faster photographic film with a consequent loss of fidelity.